Various types of molds have long been in use for preparing optical discs from thermoplastic resins. Molds for these purposes are typically manufactured from metal or a similar material having high thermal conductivity. For most purposes, high thermal conductivity is desirable since it permits the resin in the mold to cool rapidly, shortening the molding cycle time. At times, however, cooling is so rapid that the resin freezes instantaneously at the mold surface upon introduction into the mold, forming a thin solid layer which, especially if is contains a filler, can create rough surfaces, voids, porosity and high levels or residual stress and orientation. In an optical disc, such imperfections impede the optical properties and decrease or eliminate the performance of the optical disc.
Therefore, in an injection molding of compact discs, for audio, video, or computer data storage and retrieval applications, heat transfer through the mold has a strong effect on molding time and disc attributes such as birefringence, flatness, and accuracy of feature replication.
One method for affecting heat transfer and improving the cycle time during injection molding is known as the technique of managed heat transfer (MHT). The basic principle of managed heat transfer is applying a passive thermal insulating layer to the mold to control the transient heat transfer between molten resin materials and the mold surfaces during the injection molding. The insulating layer comprises materials having both low thermal diffusivity and conductivity, thus slowing the cooling of the molded resin, and good resistance to high temperature degradation, permitting use in a mold maintained at high temperatures. For improving mechanical strength, abrasion resistance, oxidation resistance and thermal conductivity, at least one skin layer may be bonded to the insulating layer.
Another method for affecting heat transfer is forming a synthetic resin layer on a stamper by coating or lamination before the stamper is placed on a core molding surface of a metal mold.
The use of a heat transfer managing layer (HTM layer) such as the thermal insulating layer and the synthetic resin layer is desirable so as to cause a minimal change in the size and shape of a molding tool and equipment. However, requirements of optical clarity, surface morphology, and replication of surface features of submicron dimensions are very stringent for optical discs. Therefore, common insulating materials, which do not provide a smooth enough surface, are not stable for long periods at the mold temperature, or cannot withstand the repeated application of high pressure during the molding process, should be avoided.
It is also difficult to apply a thick polymer coating over a 6 inch-iameter surface without defects such as particles or bubbles getting into the film surface. Particles may be generated during the spin coating process as excess materials are spun off the stamper. Particles or bubbles in the coating forms xe2x80x9chighxe2x80x9d spots on the surface of the heat transfer managing layer, which causes dimples in the molded disc, potentially forming a defective track area.
Moreover, after applying the managing heat transfer layer to the stamper, the stampers are typically punched to a final dimension required for mounting onto an injection molding equipment. This punching or trimming process also shears the polymer coating, which, if brittle, can deposit particles in the surface of the layer. These may become statically attached to the polymer surface, and are not easily removed. The punch process may also leave a raised lip around the sheared perimeter, making mounting onto the molding machine more difficult.
It is therefore desirable to provide an apparatus, stamper, and method for manufacturing data storage media. In one embodiment, the method for manufacturing data storage media comprises: disposing a managed heat transfer layer in operable communication with a second surface of a stamper, wherein a first surface of said stamper comprises surface features, wherein an exposed surface of said managed heat transfer layer has been altered by a method selected from the group consisting of chemically, mechanically, or a combination thereof; disposing the stamper in a mold with at least a portion of said exposed surface disposed in operable communication with a mold half; injecting a molten plastic into said mold; cooling the plastic to form said data storage media; and releasing said data storage media from said mold.
In one embodiment, the molding apparatus for producing data storage media comprises: a stamper comprising a managed heat transfer layer, wherein a first surface of said stamper comprises surface features, and wherein an exposed surface of said managed heat transfer layer has been altered by a method selected from the group consisting of chemically, mechanically, or a combination thereof, and has a thickness variation of less than about 5%; and a support for receiving the stamper by operable communication with said managed heat transfer layer.
In one embodiment, the method for producing a stamper, comprises: forming a nickel plated substrate having desired surface features on one side; disposing a managed heat transfer layer on a second side of said substrate; forming a thickness of said managed heat transfer layer having a variation of less than about 5%; and altering an exposed surface of said managed heat transfer layer, wherein said altering is by a method selected from the group consisting of chemically altering, mechanically altering, or a combination thereof.
The above described and other features are exemplified by the following figure and detailed description.